X-ray sensitive battery separators and related methods

ABSTRACT

The instant application relates to an X-ray sensitive battery separator for a secondary lithium battery and a method for detecting the position of a separator in a secondary lithium battery. The X-ray sensitive battery separator includes a microporous membrane having an X-ray detectable element therein, thereon, or added thereto. The X-ray detectable element constitutes less than 20% by weight of the microporous membrane or separator. The method for detecting the position of a separator in a battery, cell, stack, jellyroll, can, or the like includes the following steps: (1) providing a battery, cell, stack, jellyroll, or the like including an X-ray sensitive battery separator; (2) subjecting the battery, cell, stack, jellyroll, or the like to X-ray radiation; and (3) thereby detecting the position of said separator in said battery, cell, stack, jellyroll, or the like.

FIELD OF INVENTION

The instant application relates to X-ray sensitive or detectable batteryseparators and methods for making and using such separators, includingmethods for detecting the position of such a separator in a battery,cell, stack, jellyroll, can, or the like.

BACKGROUND OF THE INVENTION

A battery separator is used to separate the positive and negativeelectrodes of a battery, for example, in a secondary lithium battery. Abattery separator is typically microporous to allow ionic current withleast possible resistance while preventing the electrodes from directcontact resulting in an internal short.

In general, a battery separator is sandwiched between the positiveelectrode and the negative electrode of a secondary lithium battery. Itis important for a battery separator to remain in its proper positionbecause even a minute displacement may cause a short in the battery.Currently, other than as described in US Publication US2009/0081535 A1,published Mar. 26, 2009, there are no prevailing techniques to determinethe position of a separator in a battery to prevent the introduction offlawed batteries, i.e. those batteries in which the battery separator(or electrode) was displaced during the manufacturing process, into theconsumer market.

Microporous polymer membranes are known, can be made by variousprocesses, and the process by which the membrane is made may have animpact upon the membrane's physical attributes. See, for example,Kesting, Robert E., Synthetic Polymeric Membranes, A StructuralPerspective, Second Edition, John Wiley & Sons, New York, N.Y., (1985).Three different known processes for making microporous polymer membranesinclude: the dry-stretch process (also known as the CELGARD process),the wet process, and the particle stretch process.

The dry-stretch process (the CELGARD process) refers to a process wherepore formation results from stretching a nonporous, semicrystalline,extruded polymer precursor in the machine direction (MD stretch). See,for example, Kesting, Ibid. pages 290-297, incorporated herein byreference. Such a dry-stretch process is different from the wet processand the particle stretch process. Generally, in the wet process, alsoknown as the phase inversion process, the extraction process, or theTIPS process, the polymeric raw material is mixed with a processing oil(sometimes referred to as a plasticizer), this mixture is extruded, andpores are then formed when the processing oil is removed (these filmsmay be stretched before or after the removal of the oil). See, forexample, Kesting, Ibid. pages 237-286, incorporated herein by reference.

Generally, in the particle stretch process, the polymeric raw materialis mixed with a pore formation particulate, this mixture is extruded,and pores are formed during stretching when the interfaces between thepolymer and the particulate fracture due to the stretching forces. See,for example, U.S. Pat. Nos. 6,057,061 and 6,080,507, each incorporatedherein by reference.

Moreover, the membranes arising from these different formation processesare usually physically different and the process by which each is madetypically distinguishes one membrane from the other. For example,dry-stretch process membranes may have slit shaped pores due to thestretching of the precursor in the machine direction (MD stretch). Wetprocess membranes tend to have rounder pores and a lacelike appearancedue to the oil or plasticizer and the stretching of the precursor in themachine direction (MD stretch) and in the transverse machine directionor transverse direction (TD stretch). Particle stretch processmembranes, on the other hand, may have oval shaped pores as theparticulate and machine direction stretching (MD stretch) tend to formthe pores. Accordingly, each membrane may be distinguished from theother by its method of manufacture.

While membranes made by the dry-stretch process have met with excellentcommercial success, such as a variety of Celgard® dry-stretch porousmembranes sold by Celgard, LLC of Charlotte, N.C., including flat sheetmembranes, battery separators, hollow fibers, and the like, there is aneed to improve, modify or enhance at least selected physical attributesthereof, so that they may be used in a wider spectrum of applications,may perform better for particular purposes, or the like.

A modified dry-stretch process (modified CELGARD process) involving theformation of unique round shaped pores by, for example, stretching anonporous, semicrystalline, extruded polymer precursor in the machinedirection (MD stretch), followed by stretching in the transversedirection (TD stretch) with machine direction relax (MD relax) isdisclosed in US Published Application US2007/0196638 A1, published Aug.23, 2007, and incorporated by reference herein.

Despite the research efforts in developing battery separators, there maystill be a need for an improved battery separator, such as a batteryseparator which is x-ray sensitive or readily detectable when insertedor embedded in a battery, cell, stack, jellyroll, can, or the like, todetermine its position within the battery, cell, stack, jellyroll, can,or the like, or relative to the electrodes, which is relatively easy tomanufacture, is low cost, meets performance requirements, meets productspecifications, or the like. Furthermore, there may still be a need fora method for detecting the position of a separator in a battery, cell,stack, jellyroll, can, or the like to determine its position within thebattery, cell, stack, jellyroll, can, or the like, or relative to theelectrodes, which is relatively easy and cost effective, a method formanufacturing such a separator which is relatively simple and costeffective, a method for using such a separator which is relativelysimple and cost effective, or the like.

SUMMARY OF THE INVENTION

In accordance with at least selected embodiments, the instantapplication relates to an X-ray sensitive battery separator for asecondary lithium battery and a method for detecting the position ofsuch a separator in a secondary lithium battery. In accordance with atleast selected embodiments, the preferred X-ray sensitive batteryseparator includes a microporous membrane having an X-ray detectableelement. In accordance with at least selected embodiments, the X-raydetectable element constitutes a sufficient amount to detect theseparator relative to the electrodes (for example, to provide minimumcontrast in the x-ray picture). In accordance with at least particularseparator embodiments, the X-ray detectable element constitutes lessthan 20% by weight of the microporous membrane, preferably less than 15%by weight of the microporous membrane, more preferably less than 10% byweight of the microporous membrane, and most preferably less than 5% byweight of the microporous membrane.

At least an exemplary method for detecting the position of a separatorin a battery, cell, stack, jellyroll, can, or the like, includes thefollowing steps: (1) providing a battery, cell, stack, jellyroll, can,or the like including an X-ray sensitive or detectable batteryseparator; (2) subjecting the battery, cell, stack, jellyroll, can, orthe like to X-ray radiation; and (3) thereby detecting the position ofthe separator in the battery, cell, stack, jellyroll, can, or the like.

In accordance with at least selected embodiments of the presentinvention, there are provided improved battery separators, methods, orthe like, such as an improved battery separator which is x-ray sensitiveor readily detectable when inserted or embedded in a battery, cell,stack, jellyroll, can, or the like, to determine its position within thebattery, cell, stack, jellyroll, can, or the like, or to determine itsposition relative to the electrodes, which is relatively easy tomanufacture, is low cost, meets performance requirements, meets productspecifications, and/or the like. Furthermore, in accordance with atleast selected embodiments of the present invention, there are providedimproved methods for making, using, or detecting the position of aseparator in a battery, cell, stack, jellyroll, can, or the like, suchas an improved battery separator which is x-ray sensitive or readilydetectable, to determine its position within the battery, cell, stack,jellyroll, can, or the like, or relative to the electrodes, which isrelatively easy and cost effective, for manufacturing such a separatorwhich is relatively simple and cost effective, for using such aseparator which is relatively simple and cost effective, and/or thelike.

In accordance with at least certain embodiments, the instant applicationrelates to an X-ray sensitive battery separator for a secondary lithiumbattery and a method for detecting the position of such a separator in asecondary lithium battery. The X-ray sensitive battery separatorpreferably includes a microporous membrane having an X-ray detectableelement. In at least one embodiment, the X-ray detectable element, suchas barium sulfate particles, preferably constitutes less than 5% byweight of the microporous membrane. The method for detecting theposition of such a separator in a battery includes the following steps:(1) providing a battery including an X-ray sensitive battery separator;(2) subjecting the battery to X-ray radiation; and (3) thereby detectingthe position of said separator in said battery.

At least selected embodiments of the present invention relate todry-stretch X-ray sensitive or detectable battery separators and todry-stretch methods for making and methods of using such separators,including methods for detecting the position of such a separator in abattery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate to wetprocess X-ray sensitive or detectable battery separators and to wetprocess methods for making and methods of using such separators,including methods for detecting the position of such a separator in abattery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate toparticle stretch X-ray sensitive or detectable battery separators and toparticle stretch methods for making and methods of using suchseparators, including methods for detecting the position of such aseparator in a battery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate tomodified dry-stretch X-ray sensitive or detectable battery separatorsand to modified dry-stretch methods for making and methods of using suchseparators, including methods for detecting the position of such aseparator in a battery, cell, stack, jellyroll, can, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise embodiments,arrangements and instrumentalities shown.

FIG. 1 is a schematic perspective view of a first embodiment of an X-raysensitive battery separator according to the instant invention;

FIG. 2 is a schematic perspective view of second embodiment of an X-raysensitive battery separator according to the instant invention; and

FIG. 3 is an exploded view of a battery or can including the X-raysensitive battery separator of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein like numerals indicate like elements,there is shown, in FIG. 1, a first embodiment of an X-ray sensitivebattery separator 10. The X-ray sensitive battery separator 10 includesa microporous membrane 12, which contains an X-ray detectable element 14dispersed therethrough.

Microporous membrane 12 may be any microporous membrane which containsX-ray detectable element 14. Microporous membranes are generally knownin the art. Microporous membrane 12 may be made from any material, forexample a polymer. A polymer, for example, may be any synthetic polymer,cellulose, or synthetically modified cellulose. The preferred syntheticpolymers are polyolefins, e.g., polyethylene (PE), polypropylene (PP),polymethylpentene, polybutylene, ultra high molecular weightpolyethylene, ultra high molecular weight polypropylene, copolymersthereof, and mixtures or blends thereof. Microporous membrane 12 mayhave any porosity; for example, microporous membrane 12 may have aporosity in the range of about 20% to about 80%. Microporous membrane 12may have any average pore size; for example, microporous membrane 12 mayhave an average pore size in the range of about 0.1 micron to about 5microns. Microporous membrane 12 may be made of one or more plies andmay have any thickness; for example, microporous membrane 12 may have athickness in the range of about 6 microns to about 80 microns.

X-ray detectable element 14 may be any X-ray detectable material. Forexample, X-ray material 14 may be a material selected from the groupconsisting of a metal oxide, a metal phosphate, a metal carbonate, anX-ray fluorescent material, a metal sulfate or salt such as bariumsulfate (BaSO₄), and combinations thereof. The listed X-ray materialsare not limiting. Exemplary metal oxides include, but are not limitedto, metal oxides having a metal selected from the group consisting ofZn, Ti, Mn, Ba, Ni, W, Hg, Si, Cs, Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb,Cu, Ni, and Fe. The listed metal oxides are not limiting. Exemplarymetal phosphates include, but are not limited to, phosphate oxideshaving a metal selected from the group consisting of Zn, Ti, Mn, Ba, Ni,W, Hg, Si, Cs, Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Ni, and Fe. Thelisted metal phosphates are not limiting. Exemplary metal carbonatesinclude, but are not limited to, metal carbonates having a metalselected from the group consisting of Zn, Ti, Mn, Ba, Ni, W, Hg, Si, Cs,Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Ni, and Fe. The listed metalcarbonates are not limiting. Exemplary X-ray fluorescent materialsinclude, but are not limited to, organic materials, inorganic materials,and combinations thereof. A fluorescent material, as used herein, refersto a material having electrons capable of becoming exited by X-rayradiation thereby providing detection signals. The listed X-rayfluorescent materials are not limiting. X-ray detectable element 14 mayconstitute any percentage of the weight of membrane 12. For example, theX-ray detectable element may constitute in the range of 0.01 to 98percent by weight of the membrane 12, possibly preferably less than 20percent by weight of the membrane 12, more preferably less than 15percent by weight of the membrane 12, and most preferably less than 10percent by weight of the membrane 12. When barium sulfate particles areused as an x-ray detectable element, in one possibly preferredembodiment, the barium sulfate is less than 10 percent by weight of themembrane 12, possibly more preferably between 2 and 5 percent by weightof the membrane 12, and possibly most preferably about 4 percent byweight of the membrane 12.

In the alternative, referring to FIG. 2, the X-ray sensitive batteryseparator 10′ may be a multi-layer battery separator. Multi-layer, asused herein, refers to two or more layers. The X-ray detectable batteryseparator 10′ preferably includes at least one microporous membrane orlayer 12′, which contains an X-ray detectable element 14′, and at leastone other porous membrane, material or layer 16. Preferably, the X-raysensitive or detectable battery separator 10′ includes a plurality oflayers 16, for example, one on each side of layer 12′. In oneembodiment, the layer 16 is an additional layer 12′. Further, at leastone of layers 16 or 12′ or an additional layer may be a shutdown layer,i.e., one adapted to shut down ionic flow between the electrodes in theevent of thermal runaway or internal short circuiting caused by internalor external circumstances.

Microporous membrane or layer 12′ (or layers 12′) may be any microporousmembrane which contains X-ray detectable element 14′. Microporousmembranes are generally known in the art. Microporous membrane 12′ maybe made from any material, for example a polymer. A polymer, forexample, may be any synthetic polymer, cellulose, or syntheticallymodified cellulose. The preferred synthetic polymers are polyolefins,e.g., polyethylene (PE), polypropylene (PP), polymethylpentene,polybutylene, ultra high molecular weight polyethylene (UHMWPE), ultrahigh molecular weight polypropylene (UHMWPP), copolymers thereof, andmixtures or blends thereof. Microporous membrane 12′ may have anyporosity; for example, microporous membrane 12′ may have a porosity inthe range of about 20% to about 80%. Microporous membrane 12′ may haveany average pore size; for example, microporous membrane 12′ may have anaverage pore size in the range of about 0.1 micron to about 5 microns.Microporous membrane 12′ may be made of one or more plies and have anythickness; for example, microporous membrane 12′ may have a thickness inthe range of about 6 microns to about 80 microns.

X-ray detectable element 14′ (like element 14) may be any X-raydetectable material. For example X-ray material 14′ may be a materialselected from the group consisting of a metal oxide, a metal phosphate,a metal carbonate, and an X-ray fluorescent material, a metal sulfate orsalt such as barium sulfate (BaSO₄), and combinations thereof. Thelisted X-ray sensitive or detectable materials are not limiting.Exemplary metal oxides include, but are not limited to, metal oxideshaving a metal selected from the group consisting of Zn, Ti, Mn, Ba, Ni,W, Hg, Si, Cs, Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Ni, and Fe. Thelisted metal oxides are not limiting. Exemplary metal phosphatesinclude, but are not limited to, phosphate oxides having a metalselected from the group consisting of Zn, Ti, Mn, Ba, Ni, W, Hg, Si, Cs,Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Ni, and Fe. The listed metalphosphates are not limiting. Exemplary metal carbonates include, but arenot limited to, metal carbonates having a metal selected from the groupconsisting of Zn, Ti, Mn, Ba, Ni, W, Hg, Si, Cs, Sr, Ca, Rb, Ta, Zr, Al,Pb, Sn, Sb, Cu, Ni, and Fe. The listed metal carbonates are notlimiting. Exemplary X-ray fluorescent materials include, but are notlimited to, organic materials, inorganic materials, and combinationsthereof. A fluorescent material as used herein refers to a materialhaving electrons capable of becoming exited by X-ray radiation therebyproviding detection signals. The listed X-ray fluorescent materials arenot limiting. X-ray detectable element 14′ may constitute any percentageof the weight of membrane 12′. For example, the X-ray detectable element14′ may constitute in the range of 0.01 to 98 percent by weight of theseparator 10′ or membrane 12′, possibly preferably less than 20 percentby weight of the membrane 12′, more preferably less than 15 percent byweight of the membrane 12′, and most preferably less than 10 percent byweight of the membrane 12′. When barium sulfate particles are used as anx-ray detectable element, in one possibly preferred embodiment, thebarium sulfate is less than 10 percent by weight of the membrane 12′,possibly more preferably between 2 and 5 percent by weight of themembrane 12′, and possibly most preferably about 4 percent by weight ofthe membrane 12′.

Layer or layers 16 may be any conventional porous or microporousmembrane, material or layer. Porous or microporous membranes ormaterials are generally known in the art. Layer or layers 16 may be madefrom any material, for example a polymer. A polymer, for example, may beany synthetic polymer, cellulose, or synthetically modified cellulose.The preferred synthetic polymers are polyolefins, e.g., polyethylene(PE), polypropylene (PP), polymethylpentene, polybutylene, ultra highmolecular weight polyethylene, ultra high molecular weightpolypropylene, copolymers thereof, and mixtures or blends thereof. Layer16 may have any porosity; for example, layer 16 may have a porosity inthe range of about 20% to about 80%. Layer 16 may have any average poresize; for example, layer 16 may have an average pore size in the rangeof about 0.1 micron to about 5 microns. Layer 16 may be made of one ormore plies and have any thickness; for example, layer 16 may have athickness in the range of about 10 microns to about 40 microns. Whenseparator 10′ includes more than one layer 16, each such layer 16 may beof the same or different construction. As non-limiting examples,separator 10′ may have a PP layer 12′ and a PP layer 16, a PP layer 12′and a PE layer 16, a PE layer 12′ and a PP layer 16, a PE layer 12′ anda PE layer 16, a PE layer 12′ between two like PP layers 16, a PE layer12′ between two different PP layers 16, a PP layer 12′ between two likePE layers 16, a PP layer 12′ between two different PE layers 16, a PElayer 12′ between a first PP layer 16 and a second PE layer 16, two PPlayers 12′, two PP layers 12′ and a PE layer 16, two PE layers 12′, twoPE layers 12′ between two PP layers 16, or the like. Layers 12′ and 16of separator 10′, may, for example, be coextruded, laminated, or bondedtogether.

In manufacturing, referring to FIG. 3, the X-ray sensitive batteryseparator 10 of FIG. 1 (or 10′ of FIG. 2), is sandwiched between apositive electrode 18 and a negative electrode 20, and may besubsequently rolled into a jellyroll 15 (prismatic constructions orstacks, rectangular cells, pocket cells, button cells, other cans,containers, constructions, or the like, are also possible). Thejellyroll 15 may further include negative tab 24, and positive tab 22.Positive electrode 18 may include a metal sheet, e.g., aluminum foil,i.e. the current collector, upon which the positive electrode materialor electrode active mix (not shown but conventional) has been spread inconventional manner. Negative electrode 20 may include a metal sheet,e.g., copper foil, i.e. the current collector, upon which the negativeelectrode material or electrode active mix (not shown but conventional)has been spread in conventional manner. Subsequently, jellyroll 15 isinserted into can 26, which is filled with an electrolyte (not shown),and then, can 26 is sealed with cap 28 (or with a cap at each end). Can26 may be a metallic (e.g., steel, stainless steel, aluminum)cylindrical can, a plastic box, of a foil (e.g., metallized foil) pouch,or the like. Electrolyte may be any substance capable of providing ionicconductivity. Electrolyte may, for example, be a liquid electrolyte, asolid electrolyte, or a polymer or gel electrolyte. A liquid electrolytegenerally includes an electrolytic salt dissolved in a solvent, i.e. aninorganic solvent or an organic solvent. A gel electrolyte generallyincludes an electrolytic salt dissolved in non-aqueous solvent, andgelated with a polymer matrix.

In operation, a battery, cell, stack, jellyroll, can, or the likecontaining an X-ray sensitive battery separator 10 (or 10′) is subjectedto X-ray radiation thereby facilitating the detection of the position ofthe X-ray sensitive battery separator 10 (or 10′) within the battery,cell, stack, jellyroll, can, or the like. For example, the separator isusually wider than the electrodes, so that the separator extends beyondthe lateral edges of the electrodes. The separator separates and extendsbeyond the lateral edges of the electrodes to prevent the electrodesfrom coming into physical contact and thereby creating the potential forshort-circuiting. It is possible that during winding or in the batteryassembly that the separator portion that extends beyond the lateraledges of the electrodes is removed, shifted or pushed back or otherwisemisplaced (or the electrodes are moved or misplaced) thereby allowingthe possibility of physical contact of the electrodes. An X-rayexamination of the assembled battery, cell, stack, or the like allows acheck, inspection or test to determine that the separator remains (orelectrodes remain) in position throughout manufacture. The X-ray visibleseparator can be observed, via X-ray examination, to ensure that it hasmaintained its position (i.e., a portion extending beyond the lateraledges of the electrodes). Further, it is possible that the x-rayinspection process could be automated, via computer, to increase thespeed of inspection.

In accordance with at least selected possibly preferred embodiments, themembranes or layers 12, 12′, and/or 16 are made by the dry-stretchprocess (the CELGARD process) where pore formation results fromstretching a nonporous, semicrystalline, extruded polymer precursor inthe machine direction (MD stretch). See, for example, Kesting, Ibid.pages 290-297, incorporated herein by reference. Such a dry-stretchprocess is different from the wet process and the particle stretchprocess.

In accordance with at least other selected possibly preferredembodiments, the membranes or layers 12, 12′, and/or 16 are made by thewet process, also known as the phase inversion process, the extractionprocess, or the TIPS process, where the polymeric raw material is mixedwith a processing oil (sometimes referred to as a plasticizer), thismixture is extruded, and pores are then formed when the processing oilis removed (these films may be stretched before or after the removal ofthe oil). See, for example, Kesting, Ibid. pages 237-286, incorporatedherein by reference.

In accordance with at least still other selected possibly preferredembodiments, the membranes or layers 12, 12′, and/or 16 are made by theparticle stretch process, where the polymeric raw material is mixed withpore forming particulate, this mixture is extruded, and pores are formedduring stretching when the interfaces between the polymer and theparticulate fracture due to the stretching forces. See, for example,U.S. Pat. Nos. 6,057,061 and 6,080,507, each incorporated herein byreference.

In accordance with at least yet other selected possibly preferredembodiments, the membranes or layers 12, 12′, and/or 16 are made by amodified dry-stretch process (modified CELGARD process) involving, forexample, stretching a nonporous, semicrystalline, extruded polymerprecursor in the machine direction (MD stretch), followed by stretchingin the transverse direction (TD stretch) with machine direction relax(MD relax). See, for example, US Published Application US2007/0196638A1, published Aug. 23, 2007, and incorporated by reference herein.

In accordance with at least still yet other selected embodiments, themembranes or layers 12, 12′, and/or 16 are polypropylene microporousmembranes, made from a beta-nucleated precursor, or beta-nucleatedpolypropylene (BNPP) as disclosed, for example, in U.S. Pat. No.6,368,742, incorporated herein by reference. A beta-nucleating agent forpolypropylene is a substance that causes the creation of beta crystalsin polypropylene.

Further, in place of or in addition to the x-ray detectable element 14or 14′ being incorporated into the membrane or layer 12, 12′, or 16, by,for example, being mixed with the polymer prior to extrusion orformation of the precursor, membrane, film, or the like, the x-raydetectable element 14 or 14′ may be applied to the membrane or layer 12,12′, or 16, to the precursor of membrane or layer 12, 12′, or 16, may becoated on the membrane or layer 12, 12′, or 16, may be applied to themembrane or layer 12, 12′, or 16, or the like. For example, but notlimited to, barium sulfate particles may be incorporated into themembrane or layer 12, 12′, or 16, by being mixed with the polymer mixprior to extrusion or formation of the precursor, membrane, film, or thelike, may be applied to the membrane or layer 12, 12′, or 16, or to theprecursor of membrane or layer 12, 12′, or 16, may be coated on themembrane or layer 12, 12′, or 16, or may be coated on the precursor ofthe membrane or layer 12, 12′, or 16, or the like. In this way, thex-ray detectable element or elements 14 or 14′ may be incorporated into,on the surface of, applied to, and/or in the pores of the membrane orlayer 12, 12′, and/or 16. For example, but not limited to, the X-raydetectable element 14 or 14′ may be incorporated into, on the surfaceof, applied to, and/or in the pores of the membrane or layer 12 or 12′,and may constitute any percentage of the weight of membrane 12 or 12′ orof separator 10 or 10′. For example, the X-ray detectable element 14 or14′ may constitute in the range of 0.01 to 98 percent by weight of theseparator 10 or 10′ or membrane 12 or 12′, preferably less than 20percent by weight of the membrane 12 or 12′, more preferably less than15 percent by weight of the membrane 12 or 12′, and most preferably lessthan 10 percent by weight of the membrane 12 or 12′. When barium sulfateparticles are used as an x-ray detectable element, in one possiblypreferred embodiment, the barium sulfate is less than 10 percent byweight of the separator 10 or 10′ or of the membrane 12 or 12′, possiblymore preferably between 2 and 5 percent by weight of the membrane 12 or12′, and possibly most preferably about 4 percent by weight of themembrane 12 or 12′. When barium sulfate particles are used as an x-raydetectable element, in another possibly preferred embodiment, the bariumsulfate is less than 15 percent by weight of the precursor of themembrane 12 or 12′, possibly more preferably less than 10 percent byweight of the precursor, possibly preferably between 1 and 10 percent byweight of the precursor, and possibly most preferably about 7 to 8percent by weight of the precursor.

In one possible example, a porous polymer membrane 12 has a coatingincluding barium sulfate particles and a binder on one surface thereof.The weight percent of barium sulfate is preferably less than 20% byweight of the combined membrane and coating weight.

In accordance with at least selected embodiments of the presentinvention, there is provided an X-ray sensitive battery separator for asecondary lithium battery and a method for detecting the position ofsuch a separator in a secondary lithium battery. In accordance with atleast selected embodiments, the preferred X-ray sensitive batteryseparator includes a microporous membrane having an X-ray detectableelement. In accordance with at least selected embodiments, the X-raydetectable element constitutes a sufficient amount to detect theseparator relative to the electrodes (for example, to provide minimumcontrast in the x-ray picture). In accordance with at least particularseparator embodiments, the X-ray detectable element constitutes lessthan 20% by weight of the microporous membrane, preferably less than 15%by weight of the microporous membrane, more preferably less than 10% byweight of the microporous membrane, and most preferably less than 5% byweight of the microporous membrane.

At least an exemplary method for detecting the position of a separatorin a battery, cell, stack, jellyroll, can, or the like, includes thefollowing steps: (1) providing a battery, cell, stack, jellyroll, can,or the like including an X-ray sensitive or detectable batteryseparator; (2) subjecting the battery, cell, stack, jellyroll, can, orthe like to X-ray radiation; and (3) thereby detecting the position ofthe separator in the battery, cell, stack, jellyroll, can, or the like.

In accordance with at least selected embodiments of the presentinvention, there are provided improved battery separators, methods, orthe like, such as an improved battery separator which is x-ray sensitiveor readily detectable when embedded in a battery, cell, stack,jellyroll, can, or the like, to determine its position within thebattery, cell, stack, jellyroll, can, or the like, or to determine itsposition relative to the electrodes, which is relatively easy tomanufacture, is low cost, meets performance requirements, meets productspecifications, and/or the like. Furthermore, in accordance with atleast selected embodiments of the present invention, there are providedimproved methods for making, using, or detecting the position of aseparator in a battery, cell, stack, jellyroll, can, or the like, suchas an improved battery separator which is x-ray sensitive or readilydetectable, to determine its position within the battery, cell, stack,jellyroll, can, or the like, or relative to the electrodes, which isrelatively easy and cost effective, for manufacturing such a separatorwhich is relatively simple and cost effective, for using such aseparator which is relatively simple and cost effective, and/or thelike.

In accordance with at least certain embodiments, the instant applicationrelates to an X-ray sensitive battery separator for a secondary lithiumbattery and a method for detecting the position of such a separator in asecondary lithium battery. The X-ray sensitive battery separatorpreferably includes a microporous membrane having an X-ray detectableelement. The X-ray detectable element, such as barium sulfate particles,preferably constitutes less than 5% by weight of the microporousmembrane. The method for detecting the position of such a separator in abattery includes the following steps: (1) providing a battery includingan X-ray sensitive battery separator; (2) subjecting the battery toX-ray radiation; and (3) thereby visually detecting the position of saidseparator in said battery.

At least selected embodiments of the present invention relate todry-stretch X-ray sensitive or detectable battery separators and todry-stretch methods for making and methods of using such separators,including methods for detecting the position of such a separator in abattery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate to wetprocess X-ray sensitive or detectable battery separators and to wetprocess methods for making and methods of using such separators,including methods for detecting the position of such a separator in abattery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate toparticle stretch X-ray sensitive or detectable battery separators and toparticle stretch methods for making and methods of using suchseparators, including methods for detecting the position of such aseparator in a battery, cell, stack, jellyroll, can, or the like.

At least selected embodiments of the present invention relate tomodified dry-stretch X-ray sensitive or detectable battery separatorsand to modified dry-stretch methods for making and methods of using suchseparators, including methods for detecting the position of such aseparator in a battery, cell, stack, jellyroll, can, or the like.

At least selected embodiments relate to an X-ray sensitive batteryseparator for a secondary lithium battery and a method for detecting theposition of a separator in a secondary lithium battery, an X-raysensitive battery separator including at least one microporous membranehaving an X-ray detectable element therein, thereon, or added thereto,an X-ray detectable element constituting less than 20% by weight of themicroporous membrane or separator, and/or a method for detecting theposition of a separator in a battery, cell, stack, jellyroll, can, orthe like includes the following steps: (1) providing a battery, cell,stack, jellyroll, or the like including an X-ray sensitive batteryseparator; (2) subjecting the battery, cell, stack, jellyroll, or thelike to X-ray radiation; and (3) thereby detecting the position of saidseparator in said battery, cell, stack, jellyroll, or the like.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicated the scope of the invention.

We claim:
 1. A X-ray sensitive battery separator for a secondary lithiumbattery comprising: a microporous polymer membrane having a X-raydetectable element at least one of dispersed therein, coated thereon, oradded thereto, and said X-ray detectable element comprising at least 2and no more than 20 weight % of the membrane or separator.
 2. The X-raysensitive battery separator of claim 1 wherein said X-ray detectableelement comprising between 2-10 weight % of the membrane.
 3. The X-raysensitive battery separator of claim 1 wherein said X-ray detectableelement comprising between 2-5 weight % of the membrane.
 4. The X-raysensitive battery separator of claim 1 wherein said X-ray detectableelement comprising about 4 weight % of the membrane.
 5. The X-raysensitive battery separator of claim 1 wherein the X-ray detectableelement being selected from the group consisting of metal, metal oxide,metal phosphate, metal carbonate, X-ray fluorescent material, metalsalt, metal sulfate, or mixtures thereof, and any of the foregoingmetals being selected from the group consisting of Zn, Ti, Mn, Ba, Ni,W, Hg, Si, Cs, Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Fe, and mixturesthereof.
 6. The X-ray sensitive battery separator of claim 1 wherein theX-ray detectable element being barium sulfate.
 7. A secondary lithiumbattery for X-ray inspection comprising: a positive electrode, anegative electrode, a X-ray sensitive separator located between theelectrodes, and a can housing the electrodes and separator, the X-raysensitive separator comprising a microporous polymer membrane having aX-ray detectable element dispersed therein, the X-ray detectable elementcomprising at least 2 and no greater than 20 weight % of the membrane.8. The secondary lithium battery of claim 7 wherein said X-raydetectable element comprising between 2-10 weight % of the membrane. 9.The secondary lithium battery of claim 7 wherein said X-ray detectableelement comprising between 2-5 weight % of the membrane.
 10. Thesecondary lithium battery of claim 7 wherein said X-ray detectableelement comprising about 4 weight % of the membrane.
 11. The secondarylithium battery of claim 7 wherein the X-ray detectable element beingselected from the group consisting of metal, metal oxide, metalphosphate, metal carbonate, X-ray fluorescent material, metal salt,metal sulfate, or mixtures thereof, and any of the foregoing metalsbeing selected from the group consisting of Zn, Ti, Mn, Ba, Ni, W, Hg,Si, Cs, Sr, Ca, Rb, Ta, Zr, Al, Pb, Sn, Sb, Cu, Fe, and mixturesthereof.
 12. The secondary lithium battery of claim 11 wherein the X-raydetectable element being barium sulfate.
 13. The X-ray sensitive batteryseparator of claim 1 wherein said microporous polymer membrane has saidX-ray detectable element coated thereon.
 14. The X-ray sensitive batteryseparator of claim 13 wherein said X-ray detectable element coating iscoated on at least one side of said microporous polymer membrane.